Cam angle indicating circuit



2,807,7'7s- CAM: ANGLE INDlCAT-NGiCIVRCI-lll" Ralph J.,WeidnenKalamazoo, Michg., assignor to Allen Electric &` yqnipment-Company, Kalamazoo, Mich., acorporation of Michigan Application February8, 1954SerialNo.V 4085720 lThisinvention relates toa dutyfcycle meterand particularly to a device for checking the ontimevlandfoff indicatingdevice. The indicatingedevice is V.then calibrated, inI terms of:percentage` of time and'A it.- will respond to-,pulses., applied: toit., Whenever thebreaker Acontacts; are closed and it will register inamanner to indicate the totaltime that said breaker contacts:are.-c10Se;d,as-; 6.0m-

pared, to thetime. that said breaker contacts are; open.

Another. type; of :known apparatus operatesthe integrating meter by abatte-ry of constant voltage, currenty there from being. permitted toflow to lthe meterwhenthebreaker contacts. are, inone. position and beingblocked whe the. breaker contacts are inthe. other. position. 1

However, inasmuch as certain oscillatory. voltagesoccurrwhenfsaidlcontacts separate,r some of the pulses introduced I into theymeasuring system .are in` a. reverse, direction as compared to themajorpulse which elects, directlyor indirectly, the yoperation ofthemeterandhence these reverse pulses fail to inuence the indicatingdevice in; thefintended manner. Thus, to this extent/the;-instrumentsutilized .in conventional practice are-inaccurate..

Further, evenwhen the breaker. contacts..areclosed,`

there may |be. a slight voltagel drop across .them which, With sometypes ofpresent instrumentation, mayregister on the meter andcausey the.integrated reading to-be inaccurate. Since the resistancey betweenbreakerfcontacts willtvaryfrom one engineto another, thereisno--practicable way known to adjust the meter calibration to eliminatethis inaccuracy without creating other, worse, ones.

Accordingly, a principal object of the invention isto provide a earnangle indicator which will attaina maximum level ofaccuracy consistentwith economical imanufacture and simplicity of maintenance.

Awfurther object of theinvention is to provide a device, as aforesaid,which canfbe operated in substantially the same manner,V insofar as theoperator is concerned, as is nowcommon in conventional systems.

` A further object of theinventionis tor provide 'a ca m angle measuringdevice whichr may be yconnected toan ignition system without regard topolarity,

Ae further objectof this invention is to provide a cani ang-le measuringdevice whichmay be connected '-to 6, 12

vAI furtherobject' of the invention is to 'provide a device,

UnitedA States Patent 72,807,778 Patented Sept. 2,/4, 1957 l CC Y 2asaforesaid, whichv will notinvolve material additional expensemyer thatincident to present devices.,

A. fjurtherfobject of the invention is to provide a device, asaforesaid, havingr no movingpartsfotherthan calibratinsJ means: and' thenecessary meter.

Ay Afurther object4 of;` the invention.; is to provide a cam anglemeasuringfdeviee which. will measure potentials 0ecurning in theinduction. coil.y circuit; in a reverse direction in thefsamemanner asthose occurring in the principal direction:

A, further object offthe invention is to provide aV cam angle measuringdevice which will indicate yalloffrthe time during which thefbreakercontacts are closed. l

Aafurther.I object, of the invention is-to provide a cam anglemeasuring'deviee,whichvwillindicate allof `the time duringwhich-.thebreaker contacts are closediand which willsnonindiicate duringany, apprecii'tble-v part of the` time -thebreakencontacts are ope-n'.

A furtherfobject of-the invention is Y, toprovide a cam angle indicator`whichfwill: operate without disconnecting any parteci-the: automobileengine andwwithoutatectin-g operation ofrthe engine.

A` further object of the-invention is. tok provide a; device, as.aforesaid, which will requiref'a threshold voltage to: operate itwherebyito-eliminate inaccuracies due to variations. in'. resistance;`betweenI breakerv contacts and Without; introducing' other, Worse,inaccuracies.

Other objectsA and purposes ofi the invention willihe apparent` to.persons acquainted with. apparatusv off this general type upon a readingoffthe.followingfdescription and 1 inspection .of the accompanyingdrawings.

In the drawings:

'Figure' 1 is a diagrammatic, idealistic, illustration ofIthe-pulsesrfofv voltage appearing across automotivedistributorcontacts. i

Figure-Zis a: diagrammatic illustration ofa single one o f-thje voltagepulses shownin Figure 1 andillustrating the actua-l, alternating, pulsesoccurring during the-time which-itis desired tomeasure.

Figure 3 is a diagrammatic illustration of one example of circuitryembodyingthe invention.

Figure 4'is a diagrammaticA illustrationfoff another ex-Vample'of-circuitry embodying the invention.

In general, my invention-consists-in applying the voltage obtainedfromthe induction coil circuit of an automobile engine through a type ofrectifier-bridge circuit Vto an integrating-and measuring circuitconsisting ofa meter and a `source of constant potential. Thebridgecircuitvreceives voltage from the induction coil circuit and appliesitto the measuring circuit to control the activation of said'meter bysaid source `of constantpotential. .The bridge circuit'insures that allvoltage present betweenthe breakerV contactswhen the breaker contactsarev open, even though some of itis in a reverse direction, is eltectivefor controlling the integrating circuit. Thus, the meter is suppliedwith energy increments which are accurately proportioned according tothe true length of time that the breaker contacts are closed and it willaccordingly much vmore accurately represent the `correct cam angle inany given case beingjinvestigated.

Referring now to the drawings, there is illustrated schematically andideally in Figure 1 the voltage in thel induction coil circuit duringVthe periods the breaker contacts are opened and closed. Each ltime thebreaker contacts are open. a potential appears between theterrninals ofthe bridge circuit and this potentialis utilized to block the` ow ofcurrent originating in a constant voltage source and connected ,to ameter. Each time the breaker contacts areclosed, no such yblockingpotential` appears and the` source supplies current tothe meter, Themeter willfintegrat'e the increments of current thus intermittentlyDArsonval type.

`Figure `1 isa straight line and registers a uniform magnitudeof voltagewhereas, as illustrated in Figure 2,in

actual practice this :is not the case. i As the breaker contactsseparate, oscillations are set up in the induction coil circuitwhichcause alternating voltage pulses to appear in said circuit at thebeginning of each open period. Accordingly, the period A, abovementioned, actually includes a few pulses, as 2, 3 and 4 (Figure 2),which occupy `the iirst portion of the period A and it also includes thesubstantially steadyline 5. Thus, these pulses provide periods,illustrated by the shaded areas 6 and 7, within the interval beingmeasured during which there `.is no positive voltage at all applied tothe meter circuit. This `being the case, in conventional devices voltage`from the constant source is not blocked during the total time that itshouldbe blocked and current is accordingly supplied to the metercircuit for more time than it should be and the reading of the meterwill not be an accurate representation of the ratio of A/B.

Turning now to Figure 3 there is shown a voltage source 11 iwhich 1willnormally be the storage battery, or the generator, of the automobilewhose engine is being investigated. The induction coil is indicated at12 and the breaker switch is indicated at 13 driven in a conventionalmanner by the cam 14. The circuit thus far described is the circuitwithin the automobile engine which is to be tested and the informationto be ascertained is the amountof time during which the switch 13 isclosed as compared to the amountl of time that said switch 13 is open.`

For carrying out this investigation, there is provided `a bridge circuit16 comprising serially connected rectifiers 17 and 18 and comprisingalso serially connected re- `sistances 19 and 21. Said rectitiers may beof any conventional type, dry disk, tube or other. A first lead 22connects the terminal 23 of the bridge circuit 16 with one contact ofthe breaker switch 13 and a second lead 24 connects the other terminal26 of the bridge circuit 16 to the other contact `of the breaker switch13. A con rductor 27 connects the junction point 28 of the bridgecircuit 16 `to the positive side of a source of constant potential 29.Said source 29 is preferably a small, constant voltage, battery whichmay be conveniently of the type shown by PatentNo. 2,422,045, but theparticular battery `solindicated is illustrative only and not limiting.The conductor 31 then connects the negative side of said source 29` toone side of the ammeter 32. Said ammeter may be of any conventionalintegrating type, such as the The other side of said meter is connectedthrough the conductor 33` to one terminal of the variable resistance 36.The other terminal of said variable resistance is connected through therectifier 34 to the conductor 37 and thence to the junction point 38 ofAthe bridge circuit 16. The meter may be calibrated as desired. Arectifier 41 is connected at its oneside to the conductor 31 and isconnected at its other side to a point between the rectifier 34 and thejunction point 38. The polarity of the rectifier 34` is such as topermit ow of current from the junction point 38 Ito the meter 32 but `toprevent flow of current iu a reverse direction, and the polarity of therectifier 41 is such as to permit flow of current from the conductor 31to the conductor 37 and to prevent flow of current in the reversedirection.

The` operation of the device will be readily understood. When breakerswitch 13 is closed, substantially no voltage drop `exists between thecontacts thereof, and potential` between terminals 23 and 26 likewisedoes not exist. Under` theseconditions, the battery 29 will cause a flow`of current through the conductor 27 to the junction point 28 thencethrough the resistances 21 and 19 to the junction point 38,thencethrough the rectifier 34, the variable resistance 36, the meter 32 andback to the negative side of said battery.

When the breaker switch 13 is open, a voltage will appear across thecontacts thereof. The oscillations will then occur as illustrated'inFigure 2 with voltage above the reference line being taken as of suchpolarity when applied between the points 23 and 26 `of the bridgecircuit as to block flow of current from the battery 29 through themeter 32. The rectifier 18 is of such polarity as to permit flow ofcurrent from the terminal 23 to the junction point 28, i. e., in thedirection corresponding to the pulse `2. The rectifier 17 permits tlowof current from the junction'point 38 to the terminal 23, i. e., in adirection opposite to the pulse 3.

When voltage is applied to the direction indicated by the pulse 2,current flows through the conductor 22 to the terminal 23 and thence tothe junction point 28. From this junction point 28 current can thenfollow both of two paths to the terminal 26. It can ow directly throughthe resistance 21 and it can flow through the conductor 27 through thebattery 29, around the meter 32 through the rectitier 41, throughconductor 37 to the junction point 38, and finally through resistor 19to the terminal 26. The potential `producing this flow of currentopposes and overcomes the potential of the battery 29 and by reason ofthe rectifier 34 current now fails to ow through meter 32 whenever theswitch 13 is open.

An oscillation in the reverse direction, pulse 3, creates a positivepotential directing current flow through the conductor 24 to theterminal 26, thence through the resistance 21 and to the battery 29,where the same situation exists for blocking flow of current from thebattery 29 as in the case of pulse 2.

Thus, flow of current in response to the battery 29 through the meter 32is blocked whenever the breaker switch 13 is open regardless of whichway pulses flow therethrough.

Thus, each time the .breaker switch is closed, current from the battery29 `will ow through the system and energize the meter 32 and each timethe breaker switch is open, the ow of current from the battery 29 willbe blocked. In this manner, the meter registers accurately the full timethat the breaker switch is closed and the oscillations occurring at thebeginning of each opening of the breaker switch will have nodisadvantageous etect on the accuracy of the meter reading.

Further, when the voltage difference between the terminals 23 and 26 isless than one-half of the battery voltage, the presence of such avoltage difference has no effect on the ow of current from the batterythrough the meter. Thus, a small voltage drop across the breakercontacts will not atect the reading of the instrument and its accuracyis thereby still further improved.`

The variable resistance 36 is provided for calibration purposes in aknown manner.

While the foregoing described apparatus operates on the principle ofutilizing the voltage between terminals 23 and 26 to block flow from thebattery 29 although the actual circuit path is not broken, the majorpurposes of the invention will still be served by utilizing said voltageto open the battery meter circuit. Figure 4 illustrates a simple circuitof this latter nature. A switch, such as the space discharge device 40,is provided in series with the battery 29a and the meter 32a and this isrendered conductive or non-conductive by said voltage. Here the tube 40is connected into the battery-meter circuit by its principal electrodes42 and 43, its grid is connected to the negative end 38 of the bridge 16and its cathode 42 is connected also to the positive end 28 of thebridge 16. Voltage differences appearing at terminals 23 and 26 when thebreaker contacts open will block the tube 40 and when the breakercontacts are closed and substantially no voltage appears across thebridge, the tube will conduct and the meter will register. Thus themeter is caused to conduct whenever, but only whenever, the breakercontacts are closed in a generally similar manner to accomplish some ofthe sarne objectives as are set forth above in connection with the formshown in Figure 3. In this form also, a minimum, or threshold, voltageis require to effect blocking of the battery meter circuit.

While particular embodiments of the invention have been utilized forillustrative purposes, it will be appreciated that invention may bepracticed in many other specic forms and such forms are contemplatedwithin the terms of the hereinafter appended claims excepting as saidclaims may by their own terms expressly require otherwise.

I claim:

1. In a duty cycle measuring device for use with a breaker switch, thecombination comprising: an integrating meter; first and secondconductors extending from each terminal of said meter and including afirst meter circuit rectifier and a first source of D. C. potential inseries relation with each other, the polarity of said rectifier and saidfirst source being such that said rectifier will permit the passage ofcurrent flowing from rst source; a second meter circuit rectifier andcircuitry connecting said second meter circuit rectifier with said firstand second conductors in position for including said rst source and saidsecond meter circuit rectifier in series relation with each other, saidsecond meter circuit rectifier shunting said first meter circuitrectifier and said meter, the polarity of said second meter circuitrectifier being opposed to the polarity of said first source; a bridgecircuit including a pair of junction points, a pair of resistancesconnected in series between said junction points and a first bridgecircuit rectifier and a second bridge circuit rectifier connected insimilar polarity with respect to each other and in series between saidjunction points, a point between said resistances constituting one inputterminal and a point between said bridge circuit rectifiers constitutinga second input terminal, the free ends of said rst and second conductorsbeing connected respectively to said junction points and so connectedthat both of said bridge circuit rectifiers are in opposite polaritywith respect to said first source; leads extending respectively fromsaid input terminals for direct connection to the respective contacts ofsaid breaker switch; a supply circuit including a second source of D. C.potential connected to the contacts of said breaker switch, said firstsource and the resistive components of the bridge circuit being of suchmagnitude with respect to the magnitude of the potential supplied bysaid supply circuit that, when the contacts of said breaker switch areopen, the potential applied across said first source by said supplycircuit will be of value at least as great as the potential supplied bysaid first source.

2. The device defined in claim 1 including a variable resistance inseries circuit with said meter.

3. In a cam angle measuring device for use with a breaker switch,wherein the terminals of said breaker switch are connected to theignition circuit for a vehicle, the combination comprising: a pair ofinput terminals; first and second resistances, each connected at theirrespective one ends to one of said input terminals; first and secondbridge circuit rectifiers, the positive side of the first bridge circuitrectifier and the negative side of the second bridge circuit rectifierbeing connected to the other input terminal; a connection including afirst junction point connecting the negative side of said first bridgecircuit rectier with the other end of said first resistance; aconnection including a second junction point connecting the positiveside of the second bridge circuit rectifier with the other end of thesecond resistance; circuitry, including a source of D. C. potential ofpredeterminable magnitude, a meter circuit rectifier and a currentintegrating meter all serially connected directly with each other,connected to and between said junction points, the polarity of saidsource and of said meter circuit rectifier being similar with respect toeach other and opposed to that of said first and second bridge circuitrectifiers, said pair of input terminals being adapted for directconnection to the terminals of said breaker switch.

4. In a duty cycle measuring device for use with a rapidly operatingon-oft switch, the terminals of said onol switch being connected to acircuit including a D. C. potential supply, the combination comprising:a pair of inpute terminals; first and second resistances, each connectedat their respective one ends to one of said input terminals; first andsecond bridge circuit rectifiers, the positive side of the first bridgecircuit rectifier and the negative side of the second bridge circuitrectifier being connected to the other input terminal; a connectionincluding a first junction point connecting the negative side of saidfirst bridge circuit rectifier with the other end of said firstresistance; a connection including a second junction point connectingthe positive side of the second bridge circuit rectifier with the otherend of the second resistance; circuitry, including a source of D. C.potential of predeterminable magnitude, and a current integrating meterserially connected with each other and connected to and between saidjunction points, the polarity of said source being opposed to that ofsaid first and second bridge circuit rectifiers, said pair of inputterminals being adapted for direct connection to the terminals of saidrapidly operating on-of switch.

5. In a duty cycle measuring device for use with a rapidly actingswitch, the contacts of said rapidly acting switch being connected to asupply circuit whereby a first voltage is supplied to said measuringdevice or removed therefrom, depending on the condition of said rapidlyacting switch, the combination comprising: a pair of input terminalsconnected to the contacts of said switch; rst and second resistances,each connected at their respective one ends to one of said inputterminals; rst and second bridge circuit rectifiers, the positive sideof the first bridge circuit rectifier and the negative side of thesecond bridge circuit rectifier being connected to the other inputterminal; a connection including a rst junction point connecting thenegative side of said first bridge circuit rectifier with the other endof said first resistance; a connection including a second junction pointconnecting the positive side of the second bridge circuit rectifier withthe other end of the second resistance; a meter circuit including ameter and source means for constantly energizing said meter in theabsence of a minimum potential between said input terminals; connectionsrespectively extending directly between each of said junction points andsaid meter circuit for applying more than said minimum potential to saidmeter circuit of opposite polarity with respect to said source meanswhenever said rapidly acting switch is open.

References Cited in the file of this patent UNITED STATES PATENTS2,221,591 Lansdale Nov. l2, 1940 2,254,175 Eltgroth Aug. 26, 19412,312,840 Lansdale Mar. 2, 1943 2,335,247 Hanson Nov. 30, 1943 2,335,248Hanson Nov. 30, 1943 2,351,441 Makuh June 13, 1944

